1. Field of the Invention
The invention relates to a data process of an image processing apparatus for executing an error diffusion process to multivalue image data comprising a plurality of density components and outputting a result of the error diffusion process.
2. Related Background Art
Hitherto, a recording apparatus which can record an image onto recording paper on the basis of image data processed by such a kind of image processing apparatus has been proposed.
As recording elements of such a recording apparatus, various recording elements according to recording systems can be used. For example, in the case of an ink jet recording system, an ink jet recording element serving as a nozzle for emitting ink from an ink emitting port can be used. In the case of the ink jet recording system, not only the recording ink can be emitted, a picture quality improver for making a color material in the recording ink insoluble or aggregating it can be also emitted.
As an image process in the image processing apparatus as mentioned above, a quantization image process for quantizing multivalue gradation data by an error diffusion method in accordance with various methods is executed.
For example, in the image processing apparatus to execute the quantization image process for quantizing the multivalue gradation data by the error diffusion method, in the recording apparatus to which the image processing apparatus can be applied, when the inputted multigradation data is outputted to an imaging apparatus which can express it only by two gradations of 0 and 1 or by gradations of the number which is smaller than the number of gradations of the input data, the data is falsely expressed by a gradation halftone process.
As a method by which density characteristics of an inputted image can be maintained and high picture quality can be obtained, an error diffusion method (refer to a literature (Loyd. R. W. and L. Steinberg, “Adoptive Algorithm for Spatial Greyscale,”, SID Int. Sym., Digest of Tech Papers, 36, 37, 1975)) has been known.
According to such a method, a density difference between a pixel density of the input side and a pixel density of the output side which is outputted as a result of a comparison between the pixel density of the input side and a threshold value (such a threshold value is hereinafter called a quantization threshold value) is calculated. A specific weight is added to such a density difference and, thereafter, the resultant density difference is distributed to neighboring pixels. A value of such a weight (for every pixel) to the neighboring pixels or a set of such values is hereinafter called an error diffusion coefficient. By executing such a pseudo gradation expressing process as mentioned above, substantial resolution of the image which is outputted does not deteriorate but the image can be outputted at high quality.
In association with the realization of high performance of recent PCs (personal computers), as methods of improving the error diffusion method and realizing the higher picture quality, the methods disclosed in JP-A-H10-200724, JP-A-2002-51212, JP-A-H8-46784, JP-A-H8-307680, and the like can be mentioned. Those prior arts are mainly classified into the following two kinds of processes.
1) As a process regarding modulation of the error diffusion coefficient, there is a method disclosed in JP-A-H10-200724. The method is characterized in that when a value of an input signal indicates a highlight image, the error diffusion coefficient whose weight in the main scanning direction is large is used, that is, the error diffusion coefficient different from that of a normal image portion is used for a highlight image portion.
In JP-A-2002-51212, the error diffusion coefficient is set for a value of an error which is caused at the time of quantization.
2) As a process regarding modulation of the quantization threshold value, there is a method disclosed in JP-A-H8-46784. According to the method, a binarizing process is executed on the basis of a variable threshold value determined on the basis of an input density of a target pixel. According to a technique disclosed in JP-A-H8-307680, random number noises according to the input signal are added to the threshold value.
According to the error diffusion method mentioned above, a fixed value is used as an error diffusion coefficient or a quantization threshold value. On the other hand, according to those improved error diffusion methods, the error diffusion coefficient or the threshold value is made variable in accordance with a value regarding a feature of an original image such as input data, quantization error, or the like.
By those methods, reduction in (1) delay of dot appearance in the highlight portion and (2) occurrence of a periodic dot pattern at a specific gradation which became the problems in the error diffusion method mentioned above is realized. A large effect of improvement of the picture quality is obtained particularly with respect to the delay of the dot appearance in the highlight portion and occurrence of a dot chain pattern.
Hereinbelow, the error diffusion method regarding the above process 1) is called a diffusion coefficient modulation type error diffusion method and the error diffusion method regarding the above process 2) is called a threshold value modulation type error diffusion method. The inherent error diffusion method whereby the modulation of the diffusion coefficient is not executed is called a diffusion coefficient fixed type error diffusion method for convenience and the error diffusion method whereby the modulation of the threshold value is not executed is called a threshold value fixed type error diffusion method for convenience.
In recent years, the ordinary user can handle digital data of high picture quality in association with the spread of PCs of high performance and digital cameras of high precision. Consequently, a print of higher picture quality than the conventional one has been realized by using an ink jet recording apparatus or the like. It is forecasted that a demand for realizing the even higher picture quality increases in the future. Techniques to realize the high picture quality as mentioned above will become more and more important.
Meanwhile, in recent years, a demand for recording digital image data onto a medium such as paper or the like without using the PC is also increasing. First, a “WebTV” (registered trademark) system and a system such as “SetTopBox” or the like in which an Internet function is annexed to an ordinary television can be mentioned as systems which make the Internet use handy and easy. A demand for printing out the digital image data by what is called a (Non-PC) system which does not use the PC is also increasing.
In association with the spread of the digital cameras, a product which directly reads out stored data of the digital camera from a card throttle provided for a printer main body via a recording medium such as a compact flash (registered trademark) (CF) card or the like and directly performs printing without an intervention of a host PC has been realized.
Further, a product which can execute a direct printing process such that image data of the digital camera or the like is directly transmitted to the printer side by using a communication form of a universal serial bus (USB) or the like without an intervention of the recording medium such as a CF card or the like and recorded has also been realized.
In the invention, those products are called photodirect printers and a technique for realizing those functions is called a photodirect printing technique hereinbelow.
According to those photodirect printers, a controller unit to control the printer is provided in the printer and an image processing unit to execute predetermined processes to an image is also provided in the printer. The photodirect printers are generally constructed so that processes such as rendering, rasterization, color conversion, quantization, generation of a command to control the printing, and the like of the image which are executed on the host PC side in the conventional printers are executed by the image processing unit and the formed data is sent to a printer engine unit.
The printer engine unit reads out the formed data and interprets the print control command and the print data as necessary. The printer engine unit makes mechanical control such as paper feed, carriage movement, and the like which are necessary for recording the image onto an actual non-recording medium and also makes control such as applying of a recording head drive pulse, transmission of the data to a recording head, and the like.
Those controls which are made by the printer engine unit are substantially the same as those which are made when the printer engine unit receives data from the conventional host PC.
Recently, in association with the realization of the high performance of the PCs, a printer driver has been designed so that its processes on the PC are executed in a manner such that a high enough processing speed and high enough picture quality can be realized in an environment such that the PC has a memory of a large enough storing capacity of a unit of tens of megabytes and a high-speed CPU of a GHz unit.
In the Non-PC system or photodirect printer system whose demand has been increased in recent years as mentioned above, the memory of the large enough storing capacity and the high-speed CPU are not always provided for the image processes. In fact, in the Non-PC system or photodirect printer system which has been produced as a product in the market, a printing ability, particularly, speed performance of the printer engine unit cannot be effectively used due to a cause of a processing load in the controller unit.
In such an environment, in the case of using the various improved error diffusion methods mentioned above, there are the following problems.
First, if the processes of the printer driver which are executed on the PC with performance higher than that of the specification of a printer controller are executed as they are in the controller unit of the photodirect printer, a load of the image processing unit increases. Thus, a image recording speed deteriorates.
Particularly, the processing load in an error diffusion processing unit in the whole image process in the printer is generally equal to 30 to 50%. Further, the more the processing load in the various improved error diffusion methods increases, the more an influence on the whole system increases.
For example, in the technique disclosed in JP-A-10-200724 mentioned above, it is necessary that the gradation distributing unit certainly makes the discrimination about the highlight portion. Since those processes are executed to the whole inputted image, the load of the discriminating process directly influences the performance of the whole printer.
Also in the other error diffusion method mentioned above, since a process to change parameters every processing pixel is necessary, the load also increases.
In recent color ink jet printers, there are many such products in which the recording is executed by using not only the ink of four colors of C (cyan), M (magenta), Y (yellow), and K (black) but also the ink of colors of C (cyan) for a low density, M (magenta) for a low density, R (red), G (green), and B (blue) or the recording is executed by selectively using different liquid droplet amounts even in the case of the ink of the same color. With respect to those colors as well, quantization is executed separately from that for four fundamental colors of CMYK and an image is formed.
However, the concept of the colors is not disclosed in the Official Gazettes disclosing the foregoing diffusion coefficient modulation type error diffusion method and the threshold value modulation type error diffusion method mentioned above. That is, a concept that a proper data process is executed in accordance with a component such as color, liquid droplet type, or the like to be quantized (hereinafter, such a component is referred to as a quantization component or a density component) is not presumed. Naturally, a situation such that if the error diffusion process is executed without considering those components, a processing efficiency of the print data deteriorates, a print result of high picture quality cannot be obtained at a high speed, and the like is considered.